1. Field of the Invention
The present invention relates to a coating composition containing hollow particles, and in particular, to a coating composition for preparing an anti-reflection coating layer. The present invention further relates to a method for preparing the coating composition containing hollow particles.
2. Description of the Related Art
When light enters another medium from the air, a part of the light is reflected back into the air due to the difference in the refractive index of the two media, resulting in undesired glare or optical loss. Therefore, coatings and coating films with anti-reflective properties have gradually come into use in a variety of fields, for example, displays and solar energy or other photoelectric fields, for the purpose of reducing the reflection of light.
For a conventional anti-reflection coating, one or more coating layers are formed on a substrate, so that a gradient variation of the refractive index is generated between the substrate (for a glass substrate, the refractive index is about 1.52) and the air (the refractive index is about 1), so as to reduce the reflected light loss due to an excessively large difference in refractive index. In selection of coating layer materials in the prior art, addition of solid particles into a resin is widely adopted in the industry. However, since solid particles have a high refractive index, the effect of the anti-reflection coating layer prepared from them is limited.
As hollow particles have pores, the refractive index of such particles can be further reduced by an air layer or resin filled in the pores. Therefore, one focus of studies on preparation of an anti-reflection coating layer having a low refractive index has been on examining the use of hollow particles. However, compared with preparation of common solid particles, the preparation method of hollow particles is complex, expensive and difficult, making the objective of industrial production difficult to achieve.
Present methods for preparing hollow particles in the industry are based on a template method. The template method involves using a template as a core, forming a shell with a desired particle material on a surface of the template, and finally removing the template by a process such as etching or high-temperature calcination, so as to prepare a hollow particle. For example, in US Patent Publication No. 2010/0015433A1, an anti-reflection coating containing core-shell particles is first prepared, coated on a substrate, and then subjected to high-temperature treatment to remove the core material. However, the technology in which the core or template materials is removed through high-temperature heating after coating cannot be applied to a common and conventional plastic substrate such as PET, PC and PMMA, because high-temperature treatment is required.
However, in the methods for preparing hollow particles with a template, no matter whether the template is an organic polymer or inorganic material, a hydro-thermal process or a heating process is required, in which the template needs to be removed through high-temperature calcination or strong acid (for example hydrofluoric acid) or strong base corrosion, so the process is complex, expensive, and impractical for industrial production.
Chinese Patent Publication No. 1931718A discloses a method for preparing hollow silica particles, in which a sol-gel process is used to polymerize a silica precursor on a polyelectrolyte, and then the polyelectrolyte and silica are separated by repeated centrifuging and washing, so as to prepare the hollow particles. However, the process is complex, and the centrifugation that is adopted is not advantageous for industrial mass production.
In a general method for preparing an anti-reflection coating layer, for example, in a method disclosed in Chinese Patent Publication Nos. 101312909A and 1989070A, powdered hollow particles are first prepared, then mixed with an adhesive and a solvent to prepare an anti-reflection coating, and then the anti-reflection coating is applied onto a substrate to prepare a coating layer. However, the resulting hollow particles are nanoparticles, and the hollow particles are easily agglomerated during mixing due to collision and cannot retain dimensional stability. In addition, the hollow particles are required to have high dispersibility in the coating, so as to avoid non-uniform distribution in the coating layer and eliminate adverse impact on the anti-reflection effect.
In view of the above, the present invention provides an anti-reflection coating composition containing hollow particles and a method for preparing the same to solve the problems described above. The anti-reflection coating composition according to the present invention has high dispersibility, so the hollow particles can be uniformly distributed in a coating layer to exert the anti-reflection function, so as to improve light transmittance. In addition, the method according to the present invention can be carried out at normal temperature; and moreover, as the template can be removed without high-temperature heating or treatment with a strong acid or strong base, the preparation steps are effectively simplified, energy consumption is lowered, and cost is reduced, thus rendering it suitable for industrial mass production.